This invention is directed to a primer composition containing zircoaluminate coupling agent to improve adhesion of a waterborne base coat that has been applied to a layer of the primer.
Zircoaluminate coupling agents have been used as adhesion promoters in adhesives and coatings to improve the adhesion of the adhesive or coating to metal substrates as shown in Claffey et al U.S. Pat. No. 4,650,526, issued Mar. 17, 1987 and Winton et al U.S. Pat. No. 5,035,940 issued Jul. 30, 1991.
To reduce solvent emissions, many auto and truck manufacturing plants use waterborne basecoats over high solids solvent borne primers. A clear coating usually is applied over the waterborne basecoat which can be waterborne or solvent borne clear coating. Another advantage other than reduction of solvent emissions of waterborne coatings is improved appearance particularly for metallic flake containing coatings in comparison to conventional solvent borne basecoats. However, there have been intercoat adhesion failures between the waterborne basecoats and the solvent borne primers in particular solvent borne primers of polyesters, polyester urethanes and epoxy polyesters which contain monomeric and/or polymeric melamine crosslinking agents. Monomeric melamine crosslinking agents are particularly desirable since these agents form primers that have a higher solids content and lower VOC (volatile organic content) than primers made with conventional polymeric melamine crosslinking agents.
There is a need for a low VOC primer composition that upon curing has good adhesion to the substrate to which it is applied and provides a surface to which a waterborne topcoating will have excellent adherence.